Technical Field
The disclosure herein relates to a coating covering an engine or such of an aircraft, and in particular to a coating protecting the engine or such from high-temperature and oxidative environments.
Description of the Related Art
To improve various properties including energy efficiency of engines of aircrafts is a persistently remaining technical problem. While one of key factors for improving the energy efficiency is, as being well-known, weight reduction, another exemplified measure right along therewith could be elevation of the operating temperature. Operation of an engine in higher temperatures improves thermal efficiency thereof, thereby creating an expectation of improvement of energy efficiency.
While nickel-based superalloys have been used as heat-resistant materials, ceramic matrix composites (CMCs) have been recently sought to apply for the purposes of further weight reduction and improvement of heat resistance. A CMC is a material that consists of fabrics of silicon carbide (SiC) fibers embedded in a matrix of SiC (SiC/SiC) for example. There may be various combinations such C/C, C/SiC, SiC/Si3N4 and Al2O3/Al2O3.
SiC has a remarkable heat resistance and silica (SiO2) as its oxidation product can protect SiC from further oxidation. On the other hand, air sucked by the engine contains a non-negligible amount of water vapor. This water vapor could react with silica at elevated temperatures to change it into volatile hydroxides and consequently exhaustion of SiC is unavoidable. Arts for covering CMCs with some environmental barrier coatings (EBCs) are proposed in order to prevent this high temperature vapor oxidation. The following literatures disclose related arts.                United States Patent Application Publication 2003/0003328 A1        Japanese Patent Application Laid-open No. H11-12050        